Magnetic disk drives generally read and write data on the surface of a rotating magnetic disk with a transducer or “head” that is located at the far end of a moveable actuator. A servo control system uses servo control information recorded amongst the data, or on a separate disk, to controllably move the transducer from track to track (“seeking”) and to hold the transducer at a desired track (“track following”). A detailed discussion of servo control systems is unnecessary because such systems are well known as set forth, for example, in patent application Ser. No. 09/138,841 that was filed on Aug. 24, 1998, entitled “DISK DRIVE CAPABLE OF AUTONOMOUSLY EVALUATING AND ADAPTING THE FREQUENCY RESPONSE OF ITS SERVO CONTROL SYSTEM,” and is commonly owned by the assignee of this application.
The industry has previously mounted various kinds of accelerometers on the disk drive in order to sense external forces.
One example is U.S. Pat. No. 5,426,545 entitled “Active Disturbance Compensation System for Disk Drives.” This patent discloses an angular acceleration sensor that comprises an opposed pair of linear accelerometers. The overall sensor package is mounted to the HDA or drive housing, as shown in FIG. 1 of the '545 patent, in order to detect and correct for angular acceleration about the axis of the balanced actuator assembly that would otherwise produce a radial position error, as shown in FIG. 2 of the '545 patent, due to the actuator's inertial tendency to remain stationary in the presence of such acceleration.
U.S. Pat. No. 5,521,772 entitled “Disk Drive with Acceleration Rate Sensing” discloses a variation on that theme in that it uses an “acceleration rate sensor” rather than a linear acceleration sensor (conventional accelerometer) or angular acceleration sensor. The sensor is mounted to the disk drive housing.
U.S. Pat. No. 5,663,847 is yet another patent disclosing an angular accelerometer in a disk drive. It is entitled “Rejection of Disturbances on a Disk Drive by Use of an Accelerometer.” In FIG. 1, the '847 patent discloses an angular accelerometer that is mounted to the drive's base plate in order to sense rotational motion. The '847 patent is similar to the '545 patent in that both are addressing the problem that when the disk drive containing a balanced actuator is bumped rotationally in the plane of the disk, a position error will arise because “the actuator will retain its position in inertial space . . . ” (4:19-21).
PCT Application WO 97/02532 discloses another apparent use of an accelerometer that is described therein as a “shock sensor” (See FIG. 3). This application is entitled “Disk Drive Data Protection System”. According to the disclosure, the shock sensor detects “physical shocks to the disk drive which may compromise data being transferred . . . ”
The foregoing patents, however, do not effectively address the disturbance torque that may be imposed on an imbalanced actuator due to linear vibrations experienced by the disk drive during track following. There remains a need, therefore, for a disk drive with suitable provisions for canceling the effects of such vibration.